VASOACTIVE DRUGS: TYPES AND EFFECTS ON THE BRAIN - MEDICINE - 2025

The vasoactive drugs are a group of drugs used to increase blood pressure or the rate at which the heart beats of a person. In general, it is considered that there are two different types: those that have a vasopressor function and those that cause an inotropic effect.

Vasopressor drugs cause vasoconstriction; In other words, these drugs temporarily narrow the veins and arteries of the user. In this way, the person's blood pressure is artificially increased.

On the other hand, inotropic drugs are characterized by directly increasing the speed at which the person's heart beats. In this way, blood pressure also increases; however, it does so through a few different mechanisms.

Vasoactive drugs are recommended in the case of patients with shock or fainting due to lack of blood pressure. However, more studies are needed on these to decide which are the safest and what side effects they may have.

Classification

As already mentioned above, vasoactive drugs are usually classified into two different types: vasopressors, which artificially narrow the size of the person's veins and arteries; and inotropic drugs, which increase the rate at which the heart beats.

Some of these substances are generated naturally by the body, while others are synthesized in the laboratory to be used for clinical purposes. However, they all work by activating the same receptors in the brain.

Vasopressors

Vasopressors (also known as catecholamines) are a type of neurotransmitter that occurs naturally in the body and is released into the bloodstream.

Most are created from an amino acid known as tyrosine. The most important of which we generate naturally are adrenaline, dopamine and norepinephrine.

In general, these substances are generated either in the adrenal glands or in the nerve endings; therefore, they can be considered both hormones and neurotransmitters. Its effect is to activate the sympathetic nervous system, thus generating an increase in blood pressure.

These hormones can also be administered artificially to patients, in which case a synthetic version of the three present in the body can be used. However, sometimes others such as dobutamine, isoprenaline or dopexamine are also used.

Inotropic drugs

Any substance that alters the strength or energy of muscle contractions is known as an inotrope. Negative inotropes reduce the force with which muscles contract, while positive inotropes increase it.

The most common of all are those used to increase myocardial contractility; that is, the force with which the heart contracts.

However, in certain medical conditions it is also necessary to use negative inotropes to decrease the energy of the heartbeat and thus reduce tension.

There are many types of inotropic drugs, but some of the most widely used are calcium and calcium sensitizers, digoxin, phosphodiesterase inhibitors, glucagon, insulin, ephedrine, vasopressin, and some steroids.

All of these substances work by increasing the concentration of calcium within cells, or by increasing the sensitivity of calcium receptors. This causes an increase in the contractility of the heart, which can be very helpful in treating some diseases.

How do they act in the brain?

Vasopressor drugs act through an effect on the sympathetic and parasympathetic nervous systems. Both are related to the maintenance and regulation of certain bodily functions, such as blood flow and blood pressure.

In general, the parasympathetic nervous system is responsible for the conservation of the maximum possible energy and the maintenance of the functioning of the organs during periods in which the activity is not very high.

On the contrary, the parasympathetic nervous system is activated in the situations in which we are faced with a danger or a stressful situation. At that moment a series of changes takes place in our body that lead to the appearance of a response known as "fight or flight".

Both body systems are in close balance, so they often work together to keep the body functioning properly.

Operation of both systems

The mechanisms by which the sympathetic and parasympathetic nervous systems regulate blood pressure and the speed of the heartbeat are different from each other. We will describe each of these below.

The parasympathetic nervous system contributes to the regulation of the heartbeat through its influence on the vagus nerve. This is capable of slowing down the myocardial contraction, but it has no influence on the blood vessels.

On the contrary, the sympathetic nervous system has a direct influence both on the speed at which the heart beats and on the contraction of the veins and arteries.

Its main function is to keep both in a state of continuous or tonic activity. This works thanks to three types of receptors that exist in the brain.

These receptors - known as alpha, beta and dopamine receptors - are precisely those that are influenced by the action of vasopressor drugs.

In general, alpha receptors directly cause the heart muscles to contract. On the other hand, beta's cause it to dilate and allow it to contract more easily, but they do not cause the muscles to move directly. Some blood vessels are also affected by both receptors.

Effects of the most common vasopressor drugs

Now that we know which are the brain receptors that control the speed and force of contraction of the heart, we can see some examples of which of these are affected by some of the most widely used vasopressor drugs.

Epinephrine or epinephrine has a direct effect on alpha 1 and beta 1 receptors, and a lighter effect on beta 2 receptors. However, it does not elicit any response at dopamine receptors.

In contrast, dopamine causes the greatest effect on dopamine receptors (hence its name). On the other hand, it also slightly activates alpha 1 and beta 1 receptors.

Finally, norepinephrine (the last of the organically generated vasopressors in the body) is also the one that has the greatest effect: it affects alpha 1 and beta 1 receptors to a great extent, and to a lesser extent beta 2.

References

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